Parametric down conversion

To illustrate the exotic properties of "photons",
it has become fashionable to use pairs
generated by PDC (as we shall call it) instead of the
earlier generation of atomic-cascade pairs. They are
produced by causing a coherent laser beam to be
incident on a nonlinear optical crystal. If the
frequency of the laser is in the near ultraviolet
(wavelength about 300 nanometres), then the light
which emerges takes the form of a conical rainbow
of visible light (wavelengths in the range 400-800
nm)

This phenomenon is currently generally known
as parametric down conversion, but in my
opinion this is an incorrect name, because
it reflects the widely held view that a pair of
visible photons are generated by the spontaneous
decay of an ultraviolet photon from the laser. We
obtain a more correct view of this process, once we
realize that the nonlinear crystal brings about
an interaction between the laser field and the
zeropoint field, and that
as a consequence of this interaction, there is a secondary
field emitted by the crystal. In this way we are
able to understand, in an entirely classical way,
the real physical process which is occurring inside
the crystal. My preferred name for this process
is parametric amplification of the
vacuum.
Recently we have predicted that
the intensities of the waves emitted in PDC do not
exactly correspond to those of the Photon
pair-creation theory. For example, if the laser
pump has a wavelength of 267nm, then there
is a correlation between the light emitted at
400nm ("blue") and at 800nm ("red"), as in the
Photon theory. But, according to our theory, the
intensities, translated into "photons", give
1.03 red photons for every blue one. We have also
proposed an
experimental test, and, if
our prediction is confirmed, we think our
colleagues will, at last, be obliged to
accept our view that photons are now obsolete!

References

Some of the peculiar properties of PDC "photons" are described in
the following articles. Note that, in the second of
these, the authors themselves use the description
"mind-boggling", which may be taken as a synonym
for
magical.

A straightforward and scientific, that is
nonmagical, explanation of these and other
properties may be found in the following
references:

T. W. Marshall and E. Santos, The myth of the
photon, in The Present Status of the Quantum
Theory of Light
ed. S.Jeffers et al, Kluwer, Dordrecht, 1996.
This article is also on the
Quantum Physics Archive